Manufacturing seamless tubes



March 26, 1968 A. H. CALMES 3,374,650

MANUFACTURING SEAMLES S TUBES Filed Oct. 22, 1965 Pig. 2 A50 0 a 50 mo /50 200 250 afinm.)

INVENTOR. AL 5527 HE/VR/ GALA/5 BY 29 M ZA%.

A TTOIQ/VEYS United States Patent 3,374,650 MANUFACTURING SEAMLESS TUBES Albert Henri Calmes, Crans, Sierre, Valais, Switzerland,

assignor to Contubind Socit Anonyme, Lausanne,

Switzerland, a Swiss company and Lorraine-Escaut Socit Anonyme, Paris, France, a French company Filed Oct. 22, 1965, Ser. No. 501,368 Claims priority, application Great Britain, Nov. 19, 1964, 47,117/64 4 Claims. (Cl. 7246) This invention relates to the manufacture of seamless metal tubes, and more particularly to a process that forms tubes with smooth inner surfaces and uniform wall thickness.

A number of processes for manufacturing seamless tubes, such as with the plug or automatic mill, the pilger mill, the push-bench, or the continuous mill with 'a floating mandrel, are all based on rolling finished tubes from hollow blanks or shells derived from rounds or ingots pierced either on a crossroll piercing mill, a piercing press, or a combination press-piercing and rolling mill such as shown in my co-pending application, Ser. No. 379,834, filed July 2, 1964. Sometimes a secondary elongation of the shell on a second piercer or on a continuous roughing mill takes place. Due to piercing at temperatures from l220 to 1300 C. and exposure to air during travel over relatively long distances, the inner surface of such a shell is subjected to heavy secondary scaling.

Various methods are in use for improving the quality of the inner surface of a hollow shell, such as simply by throwing salt, borax and low melting silicates into the front end of the shell, but in all these cases the molten flux gathers at the bottom of the shell and therefore there is no overall coating of the inner surface. For this reason, all these quality-improving methods have had only limited or poor results when used in connection with a plug mill or extrusion press, and this also is generally true for the other processes mentioned above. In mills using long mandrels, the mandrels are lubricated with organic substances or phosphates, but the lubricants have no great efiect on scale reduction.

During rolling, loose scale sometimes is pressed into the wall of the tube or accumulates locally in depressions or cracks in the mandrel, resulting in scratches or scale pits in the tube and Wear of the mandrel. Also, due to oxidation of the inner surface, the quality of hot rolled seamless tubes has until now been generally poorer than that of welded tubes. To improve their quality it has been necessary to add a reeling operation or one or more drawing passes to smooth out their interiors.

It is among the objects of this invention to provide a process of manufacturing seamless metal tubes, in which scaling of the inner surface of a hollow shell is prevented or decreased or descaling is promoted between the piercing and rolling operations, in which smooth surfaces are produced, in which a protective flux is used that also acts as a thermal insulator and as a lubricant, and in which the shell is cooled evenly.

In accordance with this invention, a hot solid metal body is pierced to form a cylinder hollow blank that will later be formed into a tube. Protective flux, such as scale-preventing or scale-lessening flux, is distributed along the inside of the hollow blank as it is formed. The flux melts to form liquid flux, and the blank is rotated about its axis to keep the liquid flux spread over the inner peripheral surface of the hollow blank. The term rotated about its axis includes rotated down at right angles to its axis and helicoidal movement generally about it axis.

To carry out the objects of the invention a protective flux; i.e., a descaling flux, scale-dissolving flux, scale-preventing fiux or a scale-lessening flux, is used. Recom- 3,374,650 Patented Mar. 26, 1968 mended fluxes are salt, borax and their mixtures in combination with coal powder, but mixtures with glass powders, silicates and cermets may be used as well if they are required on account of steel quality, temperature and duration of rotation, as long as there is no substantial increases in friction on the mandrel due to the flux itself. The scale-lessening fluxes may include an organic substance which reduces atmospheric oxygen by combustion.

The hollow blank may be produced by forming a centering recess in one end of a solid metal body, such as a horizonal billet, filling the recess with the protective scale-preventing or scale-lessening flux, suitably in the form of a solid plug, and piercing the body to form the hollow blank, thereby distributing the flux along the inner peripheral surface of the blank. However, if desired, the flux may be applied during piercing or immediately after the withdrawal of the piercing point that was used when forming the hollow body from the solid body. For instance, the flux can be injected into the blank through orifices in a hollow bar supporting the piercing point, either during piercing or during retraction of the piercing point. Although the hollow blank preferably is tubular and open at both ends, this invention may also be used where one end of the blank is closed, such as where a push-bench is subsequently used to roll the tube. The blank, if not formed from a cylindrical body, can be rolled into cylindrical shape as it is being pierced.

It is important that the flux have a lower melting point than the metal of the blank and melt quickly to form a more or less fluid mass that can be spread out into a layer covering the inner surface of the blank. Spreading the molten flux to provide an overall continuous film is accomplished in accordance with this invention by continuously revolving the hollow blank about its axis at a speed at which centrifugal force will overcome gravity and hold the molten flux against substantially the entire area of the inner peripheral surface of the blank while awaiting the beginning of the operation of reducing and elongating the blank to form the tube. The hollow body preferably is kept in continuous rotation from the end of the piercing step to the beginning of the process step following the piercing; e.g., until it is inserted in the first stand of a tube rolling mill. Thus, the rotation of the blank will continue during transportaion of the blank to the roughing and finishing mills and during insertion into it of the lubricated mandrels on the receiving tables of those mills.

The thickness of the layer of flux may be greater 'at the bottom than at the top, the distribution depending on the viscosity of the layer and its surface tension. The protective cylindrical layer of flux can be produced if the speed of revolution of the shell is great enough to comply with the following relation:

in which n represents the speed of rotation in revolutions per minute and d represents the internal diameter of the shell in millimeters, though a lower speed of revolution may be employed in some cases, depending on the viscosity and surface tension of the liquid flux.

This process can be applied to all conventional seamless tube producing plants, but it acquires a special importance in a new process in which square billets with concave sides are pierced on a combination press-piercing and rolling mill, as disclosed in my above-mentioned co-pending patent application, prior to elongation on a roughing mill and on a finishing continuous mill using tapered hollow mandrels with controlled feed. The principal advantage of the present invention resides in preventing or lessening secondary scaling of the blank and results in less wear of the mandrels, lower energy requirements and tool consumption, and above all in the possibility of producing tubes with superior inner surfaces. A further advantage of the continuous rotation of the hollow body is that it promotes even cooling, which can result in a more uniform temperature and wall thickness than heretofore.

The invention is illustrated in the accompanying drawings, in which:

FIG. 1 is a diagrammatic end view of a horizontal hollow shell being rotated on its axis; and

FIG. 2 is 'a graph showing the relation of the rotational speed of the shell to its internal diameter.

In FIG. 1, a hot cylindrical metal blank 1, which is hollow and open at least at one end, is shown resting for instance being mounted on a carriage, or they may on a pair of rollers 2 that are rotated continuously in the same direction by any suitable means in order to revolve the blank. The rollers may be part of a conveyor system, for instance being mounted ona carriage, or they may form part of a receiving table in front of the mill in which the short blank is to be rolled into a long tube. In any case, the hollow blank is rotated fast enough to cause the flux, which was introduced into it and melted by the heat of the blank, to flow out into a fluid layer 3 that extends entirely around the inside of the blank and substantially from end to end of it to cover its inner peripheral surface. For clarity, the thickness of the layer has been exaggerated. In practice, this layer can be thin enough to prevent excessive loss of flux from the ends of the tubular blank or shell.

By following the formula given above, the desired rotational speed can be predetermined. The curve shown in the graph of FIG. 2 was plotted in accordance with that formula and shows how the minimum r.p.m. becomes less as the inside diameter of the blank increases.

Actually, a somewhat lower speed may be used in some 3 cases than indicated, depending on the viscosity of the fluid flux and the surface tension of the fluid layer.

I claim:

1. In the process of producing a seamless tube from a hot solid metal body, the steps comprising forming said body into a cylindrical hollow blank, distributing 5 meltable protective flux along the inside of said hollow blank at the time it is formed, the flux melting at a temperature substantially lower than the temperature of said body so as to form liquid fluxin the blank, as soon as said blank is formed rotating it about its axis at a speed that spreads the liquid flux out into a layer covering the inner peripheral surface of the blank, and continuing said rotation while the blank is proceeding to a subsequent step in which the blank is converted into a seamless tube.

2. In the process recited in claim 1, consuming part of the oxygen inside said hollow blank by combustion of a combustible substance mixed with the flux.

3. In the process recited in claim 1, forming said hollow blank by piercing said body to form an axial hole in it, and injecting said flux into said hole during said piercing.

4. In the process recited in claim 1, forming said hollow blank by piercing said body with a piercing point to form an axial hole in it, and injecting said flux into said hole while said point is being withdrawn.

References Cited UNITED STATES PATENTS 1,945,929 2/1934 Bark 7239 2,289,289 7/1942 Kelso 7242 2,791,924 5/1957 Sawyer 7242 3,039,888 6/ 1-962 Sejournet et al. 72--42 3,293,894 12/1966 Edgecombe et al. 7246 CHARLES W. LANI-IAM, Primary Examiner. 

1. IN THE PROCESS OF PRODUCING A SEAMLESS TUBE FROM A HOT SOLID METAL BODY, THE STEPS COMPRISING FROMING SAID BODY INTO A CYLINDRICAL HOLLOW BLANK, DISTRIBUTING MELTABLE PROTECTIVE FLUX ALONG THE INSIDE OF SAID HOLLOW BLANK AT THE TIME IT IS FORMED, THE FLUX MELTING AT A TEMPERATURE SUBSTANTIALLY LOWER THAN THE TEMPERATURE OF SAID BODY SO AS TO FORM LIQUID FLUX IN THE BLANK, AS SOON AS SAID BLANK IS FORMED ROTATING IT ABOUT ITS AXIS AT A SPEED THAT SPREADS THE LIQUID FLUX OUT INTO A LAYER COVERING THE INNER PERIPHERAL SURFACE OF THE BLANK, AND CONTINUING SAID ROTATION WHILE THE BLANK IS PROCEEDING TO A SUBSEQUENT STEP IN WHICH THE BLANK IS COVERTED INTO A SEAMLESS TUBE. 